So your proposing to drop your whole Y axis instead of having just a z axis that comes down? I'm hoping I'm interpreting your design right. I don't know, that'll add to the cost of your build and doesn't do much to strengthen your machine. Also, you'll have to be more carefull with the way you secure your stock. It would be easier to knock into something when you have the whole Y axis dropping.
Then there are the 90 degree connections, that will be some precise work that'll need to be done to get everything to square up.
I'm posting an idea you may want to look at. It would be easier and cheaper to make. Probably a little stronger. I'm not knocking your design but there are a lot of variables that would have to be considered on it.